A common type of electrical cooling fan for electronic equipment is the tubeaxial fan type, which is often relatively wide and flat in shape. This type of fan is conventionally constructed with two or more fan struts that extend across the open back of the fan between a circular support ring and the motor housing that supports the shaft of the motor, which in turn supports the fan blades. Commonly the fan struts, the ring and the motor housing are all integrally formed of a single piece that forms the rear portion of the fan and motor assembly.
Prior to the present invention it was known that bending or flexing could occur in the fan struts which would generate and transmit structureborne noise. At the same time many of these types of motor fan assemblies have a higher than desirable external magnetic field. In addition to the bending of the struts themselves, noise may be generated in the bearings, in the motor and in the resonance of other structural paths or by rotational noise and other factors.
Vibration damping adhesive material for general purpose use is formulated by a number of different suppliers. For example, the Soundcoat Company, Inc. of Deer Park, NY, provides a damping adhesive which they designate as N5. With a backing layer the designation is N5-E. This adhesive may be employed for sound damping purposes. Other suitable adhesives may be obtained from 3M Company of St. Paul, MN, which are viscoelastic polymers that are sold under the designations 468 and SJ2015X. Suitable damping adhesives sold by other manufacturers, may also be employed in conjunction with the present invention.
The present invention provides a unique structure which is formed of nickel-iron shield that fits over the supporting hub and the radial fan struts of a tubeaxial fan with an intermediate vibration damping layer of the type mentioned above, being provided between the struts and the shield. This structure provides both magnetic flux shielding and constrained-layer vibration damping for reduction of structureborne noise.